Transmitting spread signal in communication system

ABSTRACT

A method for receiving Acknowledgement/Negative acknowledgement (ACK/NACK) information in a mobile communication system includes receiving a first signal including first spread ACK/NACK information and second spread ACK/NACK information from a first antenna set of a transmitting end in an orthogonal frequency division multiplexing (OFDM) symbol; receiving a second signal including third spread ACK/NACK information and fourth spread ACK/NACK information from a second antenna set of the transmitting end in an OFDM symbol; and de-spreading at least the first and third spread ACK/NACK information or the second and fourth spread ACK/NACK information for identifying the ACK/NACK information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/166,750, filed on Jun. 22, 2011, now U.S. Pat. No. 8,369,378, whichis a continuation of U.S. patent application Ser. No. 12/139,261, filedon Jun. 13, 2008, now U.S. Pat. No. 8,009,720, which pursuant to 35U.S.C. §119, claims the benefit of earlier filing date and right ofpriority to Korean Application No. 10-2008-0007935, filed on Jan. 25,2008, and also claims the benefit of U.S. Provisional Application Ser.Nos. 60/943,783, filed on Jun. 13, 2007, 60/955,019, filed on Aug. 9,2007, 60/976,487, filed on Oct. 1, 2007, 60/982,435, filed on Oct. 25,2007, and 60/983,234, filed on Oct. 29, 2007, the contents of which areall hereby incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention relates to a mobile communication system, and moreparticularly, to transmitting a spread signal in a mobile communicationsystem.

BACKGROUND OF THE INVENTION

Recently, the demand for wireless communication services has risenabruptly due to the generalization of information communicationservices, the advent of various multimedia services and the appearanceof high-quality services. To actively cope with the demand, acommunication system's capacity should first be increased. In order todo so, methods for finding new available frequency bands and raising theefficiency of given resources in wireless communication environments areconsidered.

Much effort and attention has been made to research and developmulti-antenna technology. Here, diversity gain is obtained byadditionally securing a spatial area for resource utilization with aplurality of antennas provided to a transceiver or raising transmissioncapacity by transmitting data in parallel via each antenna.

An example of a multi-antenna technology is a multiple input multipleoutput (MIMO) scheme. The MIMO scheme indicates an antenna system havingmultiple inputs and outputs, raises a quantity of information bytransmitting different information via each transmitting antenna, andenhances reliability of transport information using coding schemes suchas STC (space-time coding), STBC (space-time block coding), SFBC(space-frequency block coding) and the like.

SUMMARY OF THE INVENTION

The present invention is directed to transmitting a spread signal in amobile communication system.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, the presentinvention is embodied in a method for transmitting a spread signal in amobile communication system, the method comprising spreading a firstsignal using a plurality of spreading codes, wherein the plurality ofspreading codes have a spreading factor, multiplexing the first spreadsignal by code division multiplexing, transmitting the first multiplexedsignal via a plurality of neighboring frequency resources of an OFDMsymbol of a first antenna set, spreading a second signal using aplurality of spreading codes, wherein the plurality of spreading codeshave a spreading factor, multiplexing the second spread signal by codedivision multiplexing, transmitting the second multiplexed signal via aplurality of neighboring frequency resources of the OFDM symbol of thefirst antenna set, transmitting the first multiplexed signal via aplurality of neighboring frequency resources of an OFDM symbol of asecond antenna set, and transmitting the second multiplexed signal via aplurality of neighboring frequency resources of the OFDM symbol of thesecond antenna set, wherein the first multiplexed signal is transmittedon frequency resources that neighbor frequency resources that the secondmultiplexed signal is transmitted on.

Preferably, the first multiplexed signal and second multiplexed signalare respectively transmitted on two neighboring frequency resources.Preferably, the spreading factor is 2.

In one aspect of the invention, the first antenna set is space frequencyblock coded by applying a space frequency block code to each neighboringpair of frequency resources of one OFDM symbol, wherein the firstantenna set comprises two antennas. In another aspect of the invention,the second antenna set is space frequency block coded by applying aspace frequency block code to each neighboring pair of frequencyresources of one OFDM symbol, wherein the second antenna set comprisestwo antennas.

Preferably, the multiplexed signals transmitted via the first antennaset and the multiplexed signals transmitted via the second antenna setare transmitted via respectively different frequency resources.Preferably, the multiplexed signals transmitted via the first antennaset and the multiplexed signals transmitted via the second antenna setare transmitted via respectively different OFDM symbols.

In a further aspect of the invention, the first multiplexed signal andsecond multiplexed signal are transmitted alternately by the firstantenna set and second antenna set via independent frequency resourcesrepeatedly. Preferably, the first multiplexed signal and secondmultiplexed signal are transmitted a total of 3 times using the firstantenna set and second antenna set alternately.

In one aspect of the invention, the first antenna set comprises a firstantenna and a second antenna of a four-antenna group, and the secondantenna set comprises a third antenna and a fourth antenna of thefour-antenna group.

In another aspect of the invention, the first antenna set comprises afirst antenna and a third antenna of a four-antenna group, and thesecond antenna set comprises a second antenna and a fourth antenna ofthe four-antenna group.

In a further aspect of the invention, the first antenna set and secondantenna set respectively comprise one antenna.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. Features, elements, and aspects of the invention that arereferenced by the same numerals in different figures represent the same,equivalent, or similar features, elements, or aspects in accordance withone or more embodiments.

FIG. 1 is a diagram explaining an example of a method for applying anSFBC/FSTD scheme in a mobile communication system in accordance with oneembodiment of the present invention.

FIG. 2 is a diagram explaining an example of a method for applying anSFBC/FSTD scheme to a spread signal in a mobile communication system inaccordance with one embodiment of the present invention.

FIG. 3 is a diagram explaining an example of a transmission structureapplicable for transmitting a spread signal in a mobile communicationsystem in accordance with one embodiment of the present invention.

FIG. 4 is a diagram explaining another example of a transmissionstructure applicable for transmitting a spread signal in a mobilecommunication system in accordance with one embodiment of the presentinvention.

FIG. 5 is a diagram explaining another example of a transmissionstructure applicable for transmitting a spread signal in a mobilecommunication system in accordance with one embodiment of the presentinvention.

FIG. 6 is a diagram explaining another example of a transmissionstructure applicable for transmitting a spread signal in a mobilecommunication system in accordance with one embodiment of the presentinvention.

FIG. 7 is a diagram explaining another example of a transmissionstructure applicable for transmitting a spread signal in a mobilecommunication system in accordance with one embodiment of the presentinvention.

FIG. 8 is a diagram explaining a further example of a transmissionstructure applicable for transmitting a spread signal in a mobilecommunication system in accordance with one embodiment of the presentinvention.

FIG. 9 is a diagram explaining an example of a transmission structureapplicable for repeatedly transmitting a spread signal in a mobilecommunication system in accordance with one embodiment of the presentinvention.

FIG. 10 is a diagram explaining another example of a transmissionstructure applicable for repeatedly transmitting a spread signal in amobile communication system in accordance with one embodiment of thepresent invention.

FIG. 11 is a diagram explaining an example of a transmission structureapplicable for transmitting a spread signal in a mobile communicationsystem in accordance with one embodiment of the present invention.

FIG. 12 is a diagram explaining another example of a transmissionstructure applicable for transmitting a spread signal in a mobilecommunication system in accordance with one embodiment of the presentinvention.

FIG. 13 is a diagram explaining an example of a method for transmittinga spread signal via a plurality of OFDM symbols in a mobilecommunication system in accordance with one embodiment of the presentinvention.

FIG. 14 is a diagram explaining an example of a method for transmittinga spread signal via a plurality of OFDM symbols in a mobilecommunication system in accordance with one embodiment of the presentinvention in which an SFBC/FSTD scheme is applied to the spread signal.

FIG. 15 is a diagram explaining an example of a method for transmittinga spread signal in a mobile communication system in accordance with oneembodiment of the present invention.

FIG. 16 is a diagram explaining an example of an apparatus for receivingAcknowledgement/Negative acknowledgement (ACK/NACK) information in amobile communication system in accordance with one embodiment of thepresent invention.

FIG. 17 is a diagram explaining an example of a method for receivingACK/NACK information in a mobile communication system in accordance withone embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to transmitting a spread signal in awireless communication system.

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. It is to be understood that the following detailed descriptionof the present invention is exemplary and explanatory and is intended toprovide further explanation of the invention as claimed. The followingdetailed description includes details to provide complete understandingof the present invention. Yet, it is apparent to those skilled in theart that the present invention can be embodied without those details.For instance, predetermined terminologies are mainly used for thefollowing description, need not to be limited, and may have the samemeaning in case of being called arbitrary terminologies.

To avoid vagueness of the present invention, the structures or devicesknown in public are omitted or depicted as a block diagram and/orflowchart focused on core functions of the structures or devices.Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like parts.

For the following embodiments, elements and features of the presentinvention are combined in prescribed forms. Each of the elements orfeatures should be considered as selective unless there is separate andexplicit mention. Each of the elements or features can be implementedwithout being combined with others. And, it is able to construct anembodiment of the present invention by combining partial elements and/orfeatures of the present invention. The order of operations explained inthe following embodiments of the present invention can be changed. Somepartial configurations or features of a prescribed embodiment can beincluded in another embodiment and/or may be replaced by correspondingconfigurations or features of another embodiment.

In this disclosure, embodiments of the present invention are describedmainly with reference to data transmitting and receiving relationsbetween a base station and a terminal. In this case, the base stationhas a meaning of a terminal node of a network, which directly performscommunication with the terminal. In this disclosure, a specificoperation described as performed by a base station can be carried out byan upper node of the base station. Namely, it is understood that variousoperations carried out by a network, which includes a plurality ofnetwork nodes including a base station, for the communication with aterminal can be carried out by the base station or other network nodesexcept the base station. “Base station” can be replaced by such aterminology as a fixed station, Node B, eNode B (eNB), access point andthe like. And, “terminal” can be replaced by such a terminology as UE(user equipment), MS (mobile station), MSS (mobile subscriber station)and the like.

Furthermore, antenna and time/frequency resource for transmittingsignals in a mobile communication system can be used in a manner ofbeing defined as a prescribed transmission structure. In the followingdescription, a transmission structure for antenna and frequency resourceis explained by considering a case that SFBC (space frequency blockcoding) scheme is applicable. Yet, the same method can be available fora transmission structure for antenna and time resource. And, it isunderstood that STBC (space time block coding) scheme is applicable tothe latter structure instead of SFBC.

FIG. 1 is a diagram explaining an example of a method for applying anSFBC/FSTD scheme in a mobile communication system, in accordance withone embodiment of the present invention. In FIG. 1, a method forobtaining 4-degree transmitting antenna diversity is implemented using aplurality of transmitting antennas, e.g., four downlink transmittingantennas of a communication system. Here, two modulation signalstransmitted via two adjacent subcarriers are transmitted via a firstantenna set including two antennas by having space frequency blockcoding (SFBC) applied thereto. Two SFBC-coded subcarrier sets aretransmitted via two different antenna sets each including two differentantennas by having frequency switching transmit diversity (FSTD) appliedthereto. As a result, a transmitting antenna diversity degree 4 can beobtained.

Referring to FIG. 1, a single small box indicates a single subcarriertransmitted via a single antenna. The letters “a”, “b”, “c” and “d”represent modulation symbols modulated into signals differing from eachother. Moreover, functions f₁(x), f₂(x), f₃(x) and f₄(x) indicate randomSFBC functions that are applied to maintain orthogonality between twosignals. These functions can be represented as in Formula 1.f ₁(x)=x,f ₂(x)=x,f ₃(x)=−x*,f ₄(x)=x*  [Formula 1]

Despite two signals being simultaneously transmitted via two antennasthrough the random SFBC function applied to maintain orthogonalitybetween the two signals, a receiving side may be able to obtain anoriginal signal by decoding each of the two signals. In particular, FIG.1 shows a structure that SFBC and FSTD transmitted in downlink within arandom time unit is repeated. By applying a simple reception algorithmthat the same SFBC decoding and FSTD decoding are repeated in areceiving side through the structure of SFBC and FSTD repeatingtransmissions, decoding complexity is reduced and decoding efficiency israised.

In the example shown in FIG. 1, modulated symbol sets (a, b), (c, d),(e, f) and (g, h) become an SFBC-coded set, respectively. FIG. 1 showsthat subcarriers having SFBC/FSTD applied thereto are consecutive.However, the subcarriers having SFBC/FSTD applied thereto may notnecessarily be consecutive in a frequency domain. For instance, asubcarrier carrying a pilot signal can exist between SFBC/FSTD appliedsubcarriers. Yet, two subcarriers constructing an SFBC coded set arepreferably adjacent to each other in a frequency domain so that wirelesschannel environments covered by a single antenna for two subcarriers canbecome similar to each other. Hence, when SFBC decoding is performed bya receiving side, it is able to minimize interference mutually affectingthe two signals.

In accordance with one embodiment of the present invention, an SFBC/FSTDscheme may be applied to a spread signal sequence. In a manner ofspreading a single signal into a plurality of subcarriers through(pseudo) orthogonal code in a downlink transmission, a plurality ofspread signals may be transmitted by a code division multiplexing (CDM)scheme. In the following description, a signal sequence spread by aprescribed spreading factor is named a spread signal.

For example, when attempting to transmit different signals “a” and “b”,if the two signals are to be CDM-transmitted by being spread by aspreading factor (SF) 2, the signal a and the signal b are transformedinto spread signal sequences (a·c₁₁, a·c₂₁) and (b·c₁₂, bc₂₂), using(pseudo) orthogonal spreading codes of two chip lengths (c₁₁, c₂₁) and(c₁₂, c₂₂), respectively. The spread signal sequences are modulated byadding a·c₁₁+b·c₁₂ and a·c₂₁+bc₂₂ to two subcarriers, respectively.Namely, a·₁₁+b·c₁₂ and a·c₂₁+bc₂₂ become modulated symbols,respectively. For clarity and convenience, the spread signal sequenceresulting from spreading the signal a by SF=N is denoted as a₁, a₂, . .. , a_(N). Furthermore, a plurality of spread signals can be multiplexedby code division multiplexing (CDM) and then transmitted.

FIG. 2 is a diagram explaining an example of a method for applying anSFBC/FSTD scheme to a spread signal in a mobile communication system, inaccordance with one embodiment of the present invention. In order todecode a signal spread over a plurality of subcarriers by despreading ina receiving side, as mentioned in the foregoing description, it ispreferable that each chip of a received spread signal sequence undergo asimilar wireless channel response. In FIG. 2, four different signals a,b, c and d are spread by SF=4 and the spread signals are transmitted bySFBC/FSTD through four subcarriers explained in the foregoingdescription of FIG. 1. Assuming that the function explained for theexample in Equation 1 is used as an SFBC function, a received signal ineach subcarrier can be represented as in Formula 2.Subcarrier 1:h ₁(a ₁ +b ₁ +c ₁ +d ₁)−h ₂(a ₂ +b ₂ +c ₂ +d ₂)*Subcarrier 2:h ₁(a ₂ +b ₂ +c ₂ +d ₂)+h ₂(a ₁ +b ₁ +c ₁ +d ₁)*Subcarrier 3:h ₁(a ₃ +b ₃ +c ₃ +d ₃)−h ₂(a ₄ +b ₄ +c ₄ +d ₄)*h ₃(a ₃ +b₃ +c ₃ +d ₃)−h ₄(a ₄ +b ₄ +c ₄ +d ₄)*Subcarrier 4:h ₁(a ₄ +b ₄ +c ₄ +d ₄)+h ₂(a ₃ +b ₃ +c ₃ +d ₃)*h ₃(a ₄ +b₄ +c ₄ +d ₄)+h ₄(a ₃ +b ₃ +c ₃ +d ₃)*  [Formula 2]

In Formula 2, h_(i) indicates fading undergone by an i^(th) antenna.Preferably, subcarriers of the same antenna undergo the same fading. Anoise component added to a receiving side may be ignored. And, a singlereceiving antenna preferably exists. In this case, spread sequencesobtained by a receiving side after completion of SFBC decoding and FSTDdecoding can be represented as in Formula 3.(|h ₁|² +|h ₂|²)·(a ₁ +b ₁ +c ₁ +d ₁),(|h ₁|² +|h ₂|²)·(a ₂ +b ₂ +c ₂ +d ₂),(|h ₃|² +|h ₄|²)·(a ₃ +b ₃ +c ₃ +d ₃),(|h ₃|² +|h ₄|²)·(a ₄ +b ₄ +c ₄ +d ₄),  [Formula 3]

Here, in order to separate the spread sequence obtained by the receivingside from the signals b, c and d by despreading with a (pseudo)orthogonal code corresponding to the signal a for example, the wirelesschannel responses for the four chips is preferably the same. However, ascan be observed from Formula 3, signals transmitted via differentantenna sets by FSTD are (|h₁|²+|h₂|²) and (|h₃|²+|h₄|²) and provideresults through different wireless channel responses, respectively.Thus, complete elimination of a different CDM-multiplexed signal duringdispreading is not performed.

Therefore, one embodiment of the present invention is directed to amethod of transmitting at least one spread signal in a communicationsystem, wherein each of at least one signal is spread by (pseudo)orthogonal code or the like with a spreading factor (SF), and whereinthe at least one spread signal is multiplexed by CDM and transmitted viathe same antenna set. FIG. 3 is a diagram explaining an example of amethod for applying an SFBC/FSTD scheme to a spread signal in acommunication system in accordance with one embodiment of the presentinvention. In the present embodiment, each of at least one signal isspread by (pseudo) orthogonal code or the like with SF=4. Furthermore,the at least one spread signal is multiplexed and transmitted by CDM,and the multiplexed signals are transmitted via the same antenna set.

In FIG. 3, when a total of four transmitting antennas are used, a firstantenna set includes a first antenna and a second antenna. A secondantenna set includes a third antenna and a fourth antenna. Inparticular, each of the first and second antenna sets is the antenna setfor performing SFBC coding, and an FSTD scheme is applicable between thetwo antenna sets. According to the present embodiment, assuming thatdata to be transmitted is carried by a single OFDM symbol, the signalspread with SF=4, as shown in FIG. 3, can be transmitted via fourneighbor subcarriers of one OFDM symbol via the same SFBC-coded antennaset.

In FIG. 3( a), shown is a case where the spread signal transmitted viathe first antenna set is different from the spread signal transmittedvia the second antenna set. In FIG. 3( b), shown is a case where thespread signal transmitted via the first antenna set is repeatedlytransmitted via the second antenna set to obtain a 4-degree transmittingantenna diversity gain.

FIG. 4 is a diagram explaining another example for a method of applyingan SFBC/FSTD scheme to a spread signal in a communication system inaccordance with one embodiment of the present invention. In FIG. 4, likethe embodiment shown in FIG. 3, each of at least one signal is spread by(pseudo) orthogonal code or the like with SF=4. The at least one spreadsignal is multiplexed and transmitted by CDM, and the multiplexedsignals are transmitted via the same antenna set.

In FIG. 4, unlike FIG. 3, when a total of four transmitting antennas areused, a first antenna set includes a first antenna and a third antenna.A second antenna set includes a second antenna and a fourth antenna.Namely, compared to FIG. 3, FIG. 4 shows a case of using a differentmethod for constructing each antenna set but applying the same SFBC/FSTDscheme. Here, according to the present embodiment, the signal spreadwith SF=4 can be transmitted via four neighbor subcarriers of one OFDMsymbol via the same SFBC-coded antenna set.

In FIG. 4( a), shown is a case where the spread signal transmitted viathe first antenna set is different from the spread signal transmittedvia the second antenna set. In FIG. 4( b), shown is a case where thespread signal transmitted via the first antenna set is repeatedlytransmitted via the second antenna set to obtain a 4-degree transmittingantenna diversity gain.

In accordance with one embodiment of the present invention, the sametransmission structure may be applied for different spreading factors.Notably, a system can use various spreading factors by considering atransport channel status, a traveling speed of terminal, a communicationenvironment and the like. According to the present embodiment, the sametransmission structure may be used for the various spreading factorsrather than separately using a specific transmission structure for aparticular spreading factor. Moreover, according to the presentembodiment, spread signals multiplexed by a CDM scheme to be transmittedvia N subcarriers are applicable even if spread by any spreading factorM smaller than N, and do not necessarily need to be spread by thespreading factor N.

For example, the transmission structure corresponding to a case wherethe spreading factor is SF=4 is applicable to various spreading factorsother than SF=4. Consequently, this lessens the complication of a systemand prevents increased signaling due to a transmission structure varyingaccording to a prescribed spreading factor.

FIG. 5 is a diagram explaining another example of a transmissionstructure applicable for transmitting a spread signal in a mobilecommunication system in accordance with one embodiment of the presentinvention. In FIG. 5, an example of a case using a total of fourtransmitting antennas is shown, wherein a first antenna set includes afirst antenna and second antenna, and a second antenna set includes athird antenna and fourth antenna.

In particular, FIG. 5( a) illustrates a case where the spread signaltransmitted via the first antenna set is different from the spreadsignal transmitted via the second antenna set. FIG. 5( b) illustrates acase where the spread signal transmitted via the first antenna set isrepeatedly transmitted via the second antenna set. Here, as mentioned inthe foregoing description, a 4-degree transmitting antenna diversitygain is obtained.

In the present embodiment, at least one signal is spread by (pseudo)orthogonal code or the like by SF=2. Moreover, the at least one signalis CDM-multiplexed and transmitted. Preferably, the present embodimentprovides a method for transmitting the multiplexed signals according tothe same transmission structure defined by SF=4.

Referring to FIG. 5, the spread signals CDM-multiplexed with foursubcarriers by SF=2 can be transmitted via two subcarriers,respectively. By applying the same transmission structure shown in FIG.3, an SFBC/FSTD transmission scheme can be applied to FIG. 5 by4-neighbor subcarrier unit of FIG. 3. However, unlike FIG. 3, a signalcan be transmitted via subcarrier in a manner that the CDM-multiplexedsignal spread by SF=2 is transmitted by 2-subcarrier unit instead of theCDM-multiplexed signal spread by SF=4.

FIG. 6 is a diagram explaining another example of a transmissionstructure applicable for transmitting a spread signal in a mobilecommunication system in accordance with one embodiment of the presentinvention. FIG. 6 differs from FIG. 5 merely by the construction of theantenna set. Thus, the same method for transmitting a spread signalshown in FIG. 5 is applied to FIG. 6.

In FIG. 6, at least one signal is spread by (pseudo) orthogonal code orthe like by SF=2. The at least one signal is CDM-multiplexed andtransmitted. Moreover, the present embodiment provides a method fortransmitting the multiplexed signals according to the same transmissionstructure defined by SF=4.

Referring to FIG. 6, the spread signals CDM-multiplexed with foursubcarriers by SF=2 can be transmitted via two subcarriers,respectively. By applying the same transmission structure shown in FIG.4, an SFBC/FSTD transmission scheme can be applied to FIG. 6 by4-neighbor subcarrier unit of FIG. 4. However, unlike FIG. 4, a signalcan be transmitted via subcarrier in a manner that the CDM-multiplexedsignal spread by SF=2 is transmitted by 2-subcarrier unit instead of theCDM-multiplexed signal spread by SF=4.

Preferably, FIGS. 5 and 6 illustrate embodiments of the presentinvention applicable to any M or N that satisfies the equation M≦N.Preferably, the present embodiment is applicable to an SFBC transmissionusing two transmitting antennas or a transmission using a singletransmitting antenna.

FIG. 7 is a diagram explaining another example of a transmissionstructure applicable for transmitting a spread signal in a mobilecommunication system in accordance with one embodiment of the presentinvention. In FIG. 7 an SFBC transmission using two transmittingantennas is shown. FIG. 7( a) illustrates a transmission structure fortransmitting spread signals CDM-multiplexed with 4 subcarriers by SF=4via four subcarriers. FIG. 7( b) illustrates a transmission structurefor transmitting spread signals CDM-multiplexed with 4 subcarriers bySF=2 via two subcarriers each.

In FIG. 7( b), data is preferably carried by subcarriers in a mannerthat the CDM-multiplexed signals spread by SF=2 instead of theCDM-multiplexed signals spread by SF=4 are transmitted by 2-subcarrierunit each. This occurs even though the SFBC transmission scheme isapplied by 4-neighbor subcarrier unit as in the transmission structureof FIG. 7( a), wherein the spread signals are spread by SF=4 accordingto the present embodiment.

FIG. 8 is a diagram explaining a further example of a transmissionstructure applicable for transmitting a spread signal in a mobilecommunication system in accordance with one embodiment of the presentinvention. In FIG. 8, a transmission uses a single transmitting antenna.FIG. 8( a) illustrates a transmission structure for transmitting spreadsignals CDM-multiplexed with 4 subcarriers by SF=4 via four subcarriers.FIG. 8( b) illustrates a transmission structure for transmitting spreadsignals CDM-multiplexed with 4 subcarriers by SF=2 via two subcarrierseach.

In FIG. 8( b), data is preferably carried by subcarriers in a mannerthat the CDM-multiplexed signals spread by SF=2 instead of theCDM-multiplexed signals spread by SF=4 are transmitted by 2-subcarrierunit each. This occurs even though the SFBC transmission scheme isapplied by 4-neighbor subcarrier unit as in the transmission structureof FIG. 8( a), wherein the spread signals are spread by SF=4 accordingto the present embodiment.

Preferably, FIGS. 7 and 8 illustrate embodiments of the presentinvention applicable to any M or N that satisfies the equation M≦N.Preferably, by applying the present embodiment to a system capable ofusing 1, 2 or 4 transmitting antennas selectively, it is advantageousfor random CDM signals or CDM signal groups to be allocated to aconsistent structure by N-subcarrier unit, e.g., 4-subcarrier unit.

In accordance with another embodiment of the present invention, a spreadsignal may be repetitively transmitted. Particularly, differentsubcarriers may be repeatedly transmitted at least one time on afrequency axis, i.e., for a period of the same time unit, such that asame signal is repeatedly transmitted to obtain additional diversity.

FIG. 9 is a diagram explaining an example of a transmission structureapplicable for repeatedly transmitting a spread signal in a mobilecommunication system in accordance with embodiment of the presentinvention. Referring to FIG. 9, an antenna-frequency mapping structurecan be repeated with a prescribed number of subcarrier intervals. Inparticular, FIG. 9 illustrates a repetitive transmission by 8-subcarrierunit, for example. By applying the SFBC/FSTD scheme through the eightneighbor subcarriers, 4-degree transmission antenna diversity gain maybe obtained. Preferably, the repetition unit constructed with eightsubcarriers in FIG. 9 includes four subcarriers for carrying a spreadsignal spread by SF=4 via a first antenna set and four subcarriers forcarrying a spread signal spread by SF=4 via a second antenna set.

Here, each of the spread signals may be a different signal or arepetitively transmitted signal. In case that each of the spread signalsis a different signal, FIG. 9 shows that each spread signal isrepeatedly transmitted three times. In case that each of the spreadsignals is a repetitively transmitted signal, FIG. 9 shows that eachspread signal is repeatedly transmitted a total of six times. Moreover,if each of the spread signals is a different signal, space diversitygain can be obtained by applying antenna set mapping of a secondrepetition unit different from a first repetition unit.

Notably, FIGS. 9( a) and 9(b) differ from each other with regard toantenna construction of the first and second antenna sets. However, thepresent embodiment may be applied to FIGS. 9( a) and 9(b) in the samemanner.

FIG. 10 is a diagram explaining another example of a transmissionstructure applicable for repeatedly transmitting a spread signal in amobile communication system in accordance with one embodiment of thepresent invention. FIG. 10 shows a method of transmitting a signalspread by SF=2 using the same transmission structure shown in FIG. 9.

Referring to FIG. 10, like FIG. 9, an antenna-frequency mappingstructure can be repeated with a prescribed number of subcarrierintervals. In particular, FIG. 10 shows a repetitive transmission by8-subcarrier unit, for example. By applying the SFBC/FSTD scheme throughthe eight neighbor subcarriers, a 4-degree transmission antennadiversity gain may be obtained.

In FIG. 10, two spread signals spread by SF=2 may be transmitted eachusing the same four subcarriers used to transmit a single spread signalspread by SF=4 in FIG. 9. In particular, the repetition unit constructedwith eight subcarriers includes four subcarriers for carrying the twospread signals spread by SF=2 via the first antenna set and foursubcarriers for carrying the spread signals spread by SF=2 each via thesecond antenna set according to the above-mentioned embodiment.Preferably, each of the spread signals may be a different signal or arepetitively transmitted signal. Moreover, antenna set mapping may bedifferently applied per repetition unit.

Notably, FIGS. 10( a) and 10(b) differ from each other with regard toantenna construction of the first and second antenna sets. However, thepresent embodiment may be applied to FIGS. 10( a) and 10(b) in the samemanner.

In accordance with another embodiment of the present invention,allocated resources may be partially used according to a transmissionstructure. Particularly, allocated resources may be used partiallyaccording to a transmission structure instead of using all resources totransmit a spread signal according to a preset transmission structure.

FIG. 11 is a diagram explaining an example of a transmission structureapplicable for transmitting a spread signal in a mobile communicationsystem in accordance with one embodiment of the present invention. InFIG. 11, a spread signal spread by SF=4 is transmitted, wherein anantenna set is determined by 4-subcarrier unit to enable a spread signalto be transmitted via the same antenna set.

Referring to FIG. 11, transmission may be performed using four of eightsubcarriers allocated by a first repetition unit according to atransmission structure instead of using all allocated resources.Moreover, transmission may be performed using four of eight subcarriersallocated by a second repetition unit. In doing so, an antenna setdifferent from that of a previous transmission may be used to implementan SFBC/FSTD scheme for obtaining 4-degree transmission antennadiversity. Preferably, as mentioned in the foregoing description, eachof the repetition units is allocated to have a prescribed number ofsubcarrier intervals.

In accordance with the present embodiment, the repetition unitconstruction does not include eight neighbor subcarriers. Instead, foursubcarriers include neighbor subcarriers, in which a prescribed numberof subcarrier intervals are inserted. And, the rest of the subcarriersinclude neighbor subcarriers. Thus, frequency diversity in addition to4-degree antenna diversity may be obtained.

In FIG. 11, four subcarriers each are configured to include neighborsubcarriers by considering an advantage that subcarriers carrying asingle spread signal include subcarriers neighboring each other. Hence,the number of subcarriers including neighbor subcarriers can be freelymodified according to the number of subcarriers used for spread signaltransmission according to a spreading factor or other reasons, purposesor the like.

Notably, FIGS. 11( a) and 11(b) differ from each other with regard toantenna construction of the first and second antenna sets. However, thepresent embodiment may be applied to FIGS. 11( a) and 11(b) in the samemanner.

FIG. 12 is a diagram explaining another example of a transmissionstructure applicable for transmitting a spread signal in a mobilecommunication system in accordance with one embodiment of the presentinvention. FIG. 12 shows a method for transmitting a spread signalspread by SF=2 using the same transmission structure shown in FIG. 11.

Referring to FIG. 12, like FIG. 11, a transmission may be performedusing four of eight subcarriers allocated by a first repetition unitaccording to a transmission structure instead of using all allocatedresources. Moreover, a transmission may be performed using four of eightsubcarriers allocated by a second repetition unit. In doing so, anantenna set different from that of a previous transmission may be usedto implement an SFBC/FSTD scheme for obtaining 4-degree transmissionantenna diversity. Preferably, as mentioned in the foregoingdescription, each of the repetition units is allocated to have aprescribed number of subcarrier intervals.

However, unlike the embodiment shown in FIG. 11, FIG. 12 illustratestransmitting a spread signal spread by SF=2, in which two spread signalsspread by SF=2 can be transmitted using four subcarriers used totransmit a single spread signal spread by SF=4. Each of the spreadsignals may be a different signal or a repetitively transmitted signal.Moreover, antenna set mapping may be applied differently per repetitionunit.

In accordance with the present embodiment, the repetition unitconstruction does not include eight neighbor subcarriers. Instead, foursubcarriers include neighbor subcarriers, in which a prescribed numberof subcarrier intervals are inserted. And, the rest of the subcarriersinclude neighbor subcarriers.

Notably, FIGS. 12( a) and 12(b) differ from each other with regard toantenna construction of the first and second antenna sets. However, thepresent embodiment may be applied to FIGS. 12( a) and 12(b) in the samemanner.

Compared to the method described with reference to FIG. 6, theembodiment of FIG. 12 saves considerable resources required forrepetitive transmission by reducing additionally used resources in half.Therefore, by applying the repetitive transmission according to thepresent embodiment, resources for data transmission are used moreefficiently.

In accordance with another embodiment of the present invention, aplurality of OFDM symbols may be applied. As described above, anSFBC/FSTD scheme was applied for a single time unit according to anembodiment of the present invention. However, transmitting a signalusing a plurality of time units may be considered. In the followingdescription, a single OFDM symbol is defined as a time unit in acommunication system adopting orthogonal frequency divisionmultiplexing. Accordingly, a method for transmitting a signal using aplurality of OFDM symbols is explained as follows.

When transmitting via a plurality of OFDM symbols, repetitivetransmission on a time axis as well as a frequency axis is possible toobtain diversity in addition to transmitting antenna diversity.Specifically, in the following description, exemplarily described is acase where CDM and SFBC/FSTD schemes are applied to a spread signal foran ACK/NAK signal transmitted in downlink to announce thesuccessful/failed reception of data transmitted in uplink.

FIG. 13 is a diagram explaining an example of a method for transmittinga spread signal via a plurality of OFDM symbols in a mobilecommunication system in accordance with one embodiment of the presentinvention. Referring to FIG. 13, each small box indicates a resourceelement (RE) constructed with a single OFDM symbol and a singlesubcarrier. A_(ij) may indicate and ACK/NAK signal multiplexed by CDM,wherein i indicates an index of a multiplexed signal after spreading,and j indicates an ACK/NAK channel index of the multiplexed ACK/NAKsignal. Here, the ACK/NAK channel indicates a set of multiplexed ACK/NAKsignals. Moreover, there can exist a plurality of ACK/NAK channelsaccording to a necessity and resource situation of each system. Forclarity and convenience of description, a single ACK/NAK channel existsin FIG. 13.

In FIG. 13( a), shown is an example where a multiplexed ACK/NAK signalis transmitted via a single OFDM symbol. Preferably, four ACK/NAKsignals are spread by a spreading factor SF=4 for a single OFDM symbol,multiplexed by CDM, and then transmitted via four neighbor subcarriers(A₁₁, A₂₁, A₃₁, A₄₁). Because a single OFDM symbol is used for theACK/NAK signal transmission, diversity gain on a time axis for theACK/NAK signal transmission may not be obtained. However, fourrepetitive transmissions of the ACK/NAK signal multiplexed by CDM alonga frequency axis may be performed. Accordingly, the four-time repetitionfacilitates diversity via repetition, wherein a repetition count variesaccording to a channel status and/or a resource status of the system.

In FIG. 13( b), shown is an example where a multiplexed ACK/NAK signalis transmitted via a plurality of OFDM symbols. Referring to FIG. 13(b), four ACK/NAK signals are spread by a spreading factor SF=4 for twoOFDM symbols each, multiplexed by CDM, and then transmitted via fourneighbor subcarriers. Preferably, when OFDM symbols for ACK/NAK signaltransmission increase, the ACK/NAK signal used for a single OFDM symbolmay be repetitively used for the increased OFDM symbols as it is.However, when the ACK/NAK signal is repetitively transmitted for asecond OFDM symbol, transmission is performed to maximize use ofsubcarriers that are not overlapped with former subcarriers used for afirst OFDM symbol. This is preferable when considering a frequencydiversity effect.

In FIG. 13( b), the number of ACK/NAK signals transmittable despite theincreased number of OFDM symbols is equal to the case of using a singleOFDM symbol. According to the present embodiment, an ACK/NAK signal,which was repeated on a frequency axis only when using a single OFDMsymbol, can be transmitted using more time-frequency resources fortransmitting the same number of ACK/NAK signals by substantiallyincrementing the repetition count of time-frequency. Here, because OFDMsymbols used for the ACK/NAK transmission are increased, more signalpower used for the ACK/NAK transmission can be allocated. Hence, theACK/NAK signal may be transmitted to a cell having a wider area.

In FIG. 13( c), shown is another example where a multiplexed ACK/NAKsignal is transmitted via a plurality of OFDM symbols. Referring to FIG.13( c), when the number of OFDM symbols for ACK/NAK signal transmissionis incremented to 2, transmission may be performed by reducing thefrequency-axis repetition count of the ACK/NAK signal multiplexed byCDM. Thus, by performing the transmission by decreasing the repetitioncount when the number of OFDM symbols is incremented to 2, resources areefficiently utilized.

Compared to the transmission method shown in FIG. 13( b), four-timefrequency-axis repetitions of ACK/NAK signal are reduced to two-timerepetitions in FIG. 13( c). However, because the number of OFDM symbolsused for ACK/NAK signal transmission is incremented, compared with thecase of using a single OFDM symbol in FIG. 13( a), FIG. 13( c) is nodifferent in that four time-frequency resource areas are available.

Compared to the method shown in FIG. 13( b), the method of FIG. 13( c)shows that signal power for ACK/NAK channel transmission may be reducedbecause the number of time-frequency resource areas used for a singleACK/NAK channel transmission is reduced. However, because the ACK/NAKchannel is transmitted across the time-frequency areas, per-symboltransmission power allocation may be performed more efficiently than thecase of transmitting via a single OFDM symbol only.

In case that ACK/NAK signals are repetitively transmitted in the samestructure for all OFDM symbols to simplify a scheduling operation on asystem, e.g., the time-frequency resources shown in FIG. 13( b) areused, different ACK/NAK channels may be transmitted. In particular,because twice as many ACK/NAK channels may be transmittable, resourcesare more efficiently used.

Preferably, a spreading factor for multiplexing a plurality of ACK/NAKsignals, a repetition count in time-frequency domain, and the number ofOFDM symbols for ACK/NAK signal transmission, which are explained withreference to FIG. 13, are exemplarily provided for a more accuratedescription of the present invention. It is understood that differentspreading factors, different repetition counts and various OFDM symbolnumbers are applicable to the present invention. Moreover, theembodiment shown in FIG. 13 relates to using a single transmittingantenna not using transmitting antenna diversity, but is also applicableto a 2-transmitting antenna diversity method, a 4-transmitting antennadiversity method, and the like.

FIG. 14 is a diagram explaining an example of a method for transmittinga spread signal via a plurality of OFDM symbols in a mobilecommunication system in accordance with one embodiment of the presentinvention, wherein an SFBC/FSTD scheme is applied to the spread signal.Preferably, an embodiment for implementing a 4-degree transmittingantenna diversity effect using a total of four transmitting antennas isexplained with reference to FIG. 14. For clarity and convenience ofdescription, a single ACK/NAK channel exists.

In FIG. 14( a), an SFBC/FSTD scheme is applied to a spread signal usingfour transmitting antennas and the signal is transmitted for a pluralityof OFDM symbols. Four ACK/NAK signals are spread by a spreading factorSF=4 for two OFDM symbols each, multiplexed by CDM, and then transmittedvia four neighbor subcarriers. Preferably, when OFDM symbols for ACK/NAKsignal transmission increase, the ACK/NAK signal used for a single OFDMsymbol may be repetitively used for the increased OFDM symbols as it is.This is similar to the process described with reference to FIG. 13 (b).

However, when a repetitive transmission is carried out for a second OFDMsymbol, transmission is performed using an antenna set different from anantenna set used for a first OFDM symbol. For example, if a transmissionfor a first OFDM symbol is performed using a first antenna set includinga first antenna and third antenna, a transmission for a second OFDMsymbol may be performed using a second antenna set including a secondantenna and fourth antenna. Preferably, transmission is performed tomaximize use of subcarriers that are not overlapped with formersubcarriers used for the first OFDM symbol. This is preferable whenconsidering a frequency diversity effect.

In FIG. 14( b), shown is another example of applying an SFBC/FSTD schemeto a spread signal using four transmitting antennas and transmitting thesignal for a plurality of OFDM symbols. Preferably, when the number ofOFDM symbols for ACK/NAK signal transmission is incremented to 2, thesignal may be transmitted by reducing a frequency-axis repetition countof the ACK/NAK signal multiplexed by CDM. This is similar to the processdescribed with reference to FIG. 13( c). However, when repetitivetransmission is performed for a second OFDM symbol, the transmissionwill be carried out using an antenna set different from an antenna setused for the first OFDM symbol.

In the above description of the examples shown in FIGS. 13 and 14, thesignal spread by SF=4 is transmitted via at least one OFDM symbol only.However, the present embodiment is applicable to a case of using severalOFDM symbols in case of a spreading factor SF=2. Preferably, for thespreading factor SF=2, two spread signals spread by SF=2 are transmittedeach using two of four subcarriers allocated to transmit a spread signalspread by SF=4. Alternatively, a two-time repetition method isapplicable thereto.

In case of transmission via several OFDM symbols, repetition on a timeaxis as well as a frequency axis is applicable to obtain diversity inaddition to transmitting antenna diversity. The above embodiments areprovided to explain the applications of the present invention and arealso applicable to a system using an SFBC/FSTD transmission diversitymethod regardless of various spreading factors (SF), various OFDM symbolnumbers and repetition counts on time and frequency axes.

FIG. 15 is a diagram explaining an example of a method for transmittinga spread signal in a mobile communication system in accordance with oneembodiment of the present invention. Referring to FIG. 15, a firstsignal is spread using a plurality of spreading codes, wherein theplurality of spreading codes have a spreading factor (S1502). The firstspread signal is multiplexed by code division multiplexing (S1504).Similarly, a second signal is spread using a plurality of spreadingcodes, wherein the plurality of spreading codes have a spreading factor(S1506). The second spread signal is multiplexed by code divisionmultiplexing (S1508). The first and second multiplexed signals aretransmitted, wherein the first multiplexed signal is transmitted onfrequency resources that neighbor frequency resources that the secondmultiplexed signal is transmitted on (S1510). The first and secondmultiplexed signals are transmitted via frequency resources of an OFDMsymbol of a first antenna set and a second antenna set.

FIG. 16 is a diagram explaining an example of an apparatus for receivingACK/NACK information in a mobile communication system in accordance withone embodiment of the present invention. Referring to FIG. 16, theapparatus (1600), such as a user equipment, comprises a plurality ofantennas (1602), a radio frequency unit (1604), and a processor (1606).The processor (1606) is configured to carry out various operationsexemplified in the specification and drawings.

FIG. 17 is a diagram explaining an example of a method for receivingACK/NACK information in a mobile communication system in accordance withone embodiment of the present invention. Referring to FIG. 16 and FIG.17, the apparatus (1600) receives a first signal including first spreadACK/NACK information and second spread ACK/NACK information from a firstantenna set of a transmitting end in an orthogonal frequency divisionmultiplexing (OFDM) symbol (S1702); receives a second signal includingthird spread ACK/NACK information and fourth spread ACK/NACK informationfrom a second antenna set of the transmitting end in an OFDM symbol(S1704); and de-spread at least the first and third spread ACK/NACKinformation or the second and fourth spread ACK/NACK information foridentifying the ACK/NACK information (S1706).

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

Embodiments of the present invention can be implemented by variousmeans, e.g., hardware, firmware, software, and any combination thereof.In case of the implementation by hardware, a method of transmitting aspread signal in a communication system according to one embodiment ofthe present invention can be implemented by at least one of applicationspecific integrated circuits (ASICs), digital signal processors (DSPs),digital signal processing devices (DSPDs), programmable logic devices(PLDs), field programmable gate arrays (FPGAs), a processor, acontroller, a microcontroller, a microprocessor, etc.

In case of implementation by firmware or software, a method oftransmitting a spread signal in a communication system according to oneembodiment of the present invention can be implemented by a module,procedure, function and the like capable of performing the abovementioned functions or operations. Software code is stored in a memoryunit and can be driven by a processor. The memory unit is providedwithin or outside the processor to exchange data with the processor byvarious means known in public.

The foregoing embodiments and advantages are merely exemplary and arenot to be construed as limiting the present invention. The presentteaching can be readily applied to other types of apparatuses. Thedescription of the present invention is intended to be illustrative, andnot to limit the scope of the claims. Many alternatives, modifications,and variations will be apparent to those skilled in the art. In theclaims, means-plus-function clauses are intended to cover the structuredescribed herein as performing the recited function and not onlystructural equivalents but also equivalent structures.

What is claimed is:
 1. A method for receiving Acknowledgement/Negativeacknowledgement (ACK/NACK) information in a mobile communication system,the method comprising: receiving a first signal including first spreadACK/NACK information and second spread ACK/NACK information from a firstantenna set of a transmitting end in an orthogonal frequency divisionmultiplexing (OFDM) symbol; receiving a second signal including thirdspread ACK/NACK information and fourth spread ACK/NACK information froma second antenna set of the transmitting end in an OFDM symbol; andde-spreading at least the first and third spread ACK/NACK information orthe second and fourth spread ACK/NACK information for identifying theACK/NACK information, wherein the first spread ACK/NACK information, thesecond spread ACK/NACK information, the third spread ACK/NACKinformation, and the fourth spread ACK/NACK information exist in a formas shown in Table 1: TABLE 1 four available neighboring subcarriers thefirst antenna A a₁ a₂  b₁ b₂  antenna set antenna B −a₂* a₁* −b₂* b₁*the second antenna C c₁ c₂  d₁ d₂  antenna set antenna D −c₂* c₁* −d₂*d₁*

wherein a₁ to a₂ are elements of the first spread ACK/NACK information,b₁ to b₂ are elements of the second spread ACK/NACK information, c₁ toc₂ are elements of the third spread ACK/NACK information, d₁ to d₂ areelements of the fourth spread ACK/NACK information, and the symbol *denotes a conjugate operation, wherein the first spread ACK/NACKinformation is generated by spreading of first ACK/NACK informationusing a first orthogonal sequence with a spreading factor of 2, whereinthe second spread ACK/NACK information is generated by spreading ofsecond ACK/NACK information using a second orthogonal sequence with aspreading factor of 2, wherein the third spread ACK/NACK information isgenerated by spreading of the first ACK/NACK information using the firstorthogonal sequence, wherein the fourth spread ACK/NACK information isgenerated by spreading of the second ACK/NACK information using thesecond orthogonal sequence, and wherein the four available neighboringsubcarriers for the first and second spread ACK/NACK information are notcontiguous with the four available neighboring subcarriers for the thirdand fourth spread ACK/NACK information in a frequency domain.
 2. Themethod of claim 1, wherein the four available neighboring subcarriersfor the first and second spread ACK/NACK information and the fouravailable neighboring subcarriers for the third and fourth spreadACK/NACK information exist on different OFDM symbols.
 3. The method ofclaim 1, further comprising: receiving a third signal including fifthspread ACK/NACK information and sixth spread ACK/NACK information fromthe first antenna set of the transmitting end in an OFDM symbol; andde-spreading at least the fifth spread ACK/NACK information or the sixthspread ACK/NACK spread information for identifying the ACK/NACKinformation, wherein the fifth and sixth spread ACK/NACK informationexist in a form as shown in Table 1 in which a₁ to a₂ and b₁ to b₂ arereplaced with e₁ to e₂ and f₁ to f₂, respectively, wherein e₁ to e₂ areelements of the fifth spread ACK/NACK information, wherein f₁ to f₂ areelements of the sixth spread ACK/NACK information, and wherein the fouravailable neighboring subcarriers for the first and second spreadACK/NACK information are not contiguous with the four availableneighboring subcarriers for the fifth and sixth spread ACK/NACKinformation in a frequency domain.
 4. The method of claim 1, wherein theantennas A and B are first two contiguously numbered antennas, and theantennas C and D are second two contiguously numbered antennas.
 5. Themethod of claim 1, wherein the antennas A and B are odd-numberedantennas, and the antennas C and D are even-numbered antennas.
 6. A userequipment configured to receive Acknowledgement/Negative acknowledgement(ACK/NACK) information in a mobile communication system, the userequipment comprising: a radio frequency unit; and a processor, whereinthe processor is adapted to: receive a first signal including firstspread ACK/NACK information and second spread ACK/NACK information froma first antenna set of a transmitting end in an orthogonal frequencydivision multiplexing (OFDM) symbol; receive a second signal includingthird spread ACK/NACK information and fourth spread ACK/NACK informationfrom a second antenna set of the transmitting end in an OFDM symbol; andde-spread at least the first and third spread ACK/NACK information orthe second and fourth spread ACK/NACK information for identifying theACK/NACK information, wherein the first spread ACK/NACK information, thesecond spread ACK/NACK information, the third spread ACK/NACKinformation, and the fourth spread ACK/NACK information exist in a formas shown in Table 1: TABLE 1 four available neighboring subcarriers thefirst antenna A a₁ a₂  b₁ b₂  antenna set antenna B −a₂* a₁* −b₂* b₁*the second antenna C c₁ c₂  d₁ d₂  antenna set antenna D −c₂* c₁* −d₂*d₁*

wherein a₁ to a₂ are elements of the first spread ACK/NACK information,b₁ to b₂ are elements of the second spread ACK/NACK information, c₁ toc₂ are elements of the third spread ACK/NACK information, d₁ to d₂ areelements of the fourth spread ACK/NACK information, and the symbol *denotes a conjugate operation, wherein the first spread ACK/NACKinformation is generated by spreading of first ACK/NACK informationusing a first orthogonal sequence with a spreading factor of 2, whereinthe second spread ACK/NACK information is generated by spreading ofsecond ACK/NACK information using a second orthogonal sequence with aspreading factor of 2, wherein the third spread ACK/NACK information isgenerated by spreading of the first ACK/NACK information using the firstorthogonal sequence, wherein the fourth spread ACK/NACK information isgenerated by spreading of the second ACK/NACK information using thesecond orthogonal sequence, and wherein the four available neighboringsubcarriers for the first and second spread ACK/NACK information are notcontiguous with the four available neighboring subcarriers for the thirdand fourth spread ACK/NACK information in a frequency domain.
 7. Theuser equipment of claim 6, wherein the four available neighboringsubcarriers for the first and second spread ACK/NACK information and thefour available neighboring subcarriers for the third and fourth spreadACK/NACK information exist on different OFDM symbols.
 8. The userequipment of claim 6, wherein the processor is further configured to:receive a third signal including fifth spread ACK/NACK information andsixth spread ACK/NACK information from the first antenna set of thetransmitting end in an OFDM symbol; and de-spread at least the fifthspread ACK/NACK information or the sixth spread ACK/NACK spreadinformation for identifying the ACK/NACK information, wherein the fifthand sixth spread ACK/NACK information exist in a form as shown in Table1 in which a₁ to a₂ and b₁ to b₂ are replaced with e₁ to e₂ and f₁ tof₂, respectively, wherein e₁ to e₂ are elements of the fifth spreadACK/NACK information, wherein f₁ to f₂ are elements of the sixth spreadACK/NACK information, wherein the four available neighboring subcarriersfor the first and second spread ACK/NACK information are not contiguouswith the four available neighboring subcarriers for the fifth and sixthspread ACK/NACK information in a frequency domain.
 9. The user equipmentof claim 6, wherein the antennas A and B are first two contiguouslynumbered antennas, and the antennas C and D are second two contiguouslynumbered antennas.
 10. The user equipment of claim 6, wherein theantennas A and B are odd-numbered antennas, and the antennas C and D areeven-numbered antennas.